Types of wireless networks include infrastructure-based wireless networks and ad hoc wireless networks.
Ad hoc networks are self-forming networks which can operate in the absence of any fixed infrastructure, and in some cases the ad hoc network is formed entirely of mobile nodes. An ad hoc network typically includes a number of geographically-distributed, potentially mobile units, sometimes referred to as “nodes,” which are wirelessly connected to each other by one or more links (e.g., radio frequency communication channels). The nodes can communicate with each other over a wireless media without the support of an infrastructure-based or wired network. Links or connections between these nodes can change dynamically in an arbitrary manner as existing nodes move within the ad hoc network, as new nodes join or enter the ad hoc network, or as existing nodes leave or exit the ad hoc network. Because the topology of an ad hoc network can change significantly techniques are needed which can allow the ad hoc network to dynamically adjust to these changes. Due to the lack of a central controller, many network-controlling functions can be distributed among the nodes such that the nodes can self-organize and reconfigure in response to topology changes.
One characteristic of the nodes is that each node can directly communicate over a short range with nodes which are a single “hop” away. Such nodes are sometimes referred to as “neighbor nodes.” When a node transmits packets to a destination node and the nodes are separated by more than one hop (e.g., the distance between two nodes exceeds the radio transmission range of the nodes, or a physical barrier is present between the nodes), the packets can be relayed via intermediate nodes (“multi-hopping”) until the packets reach the destination node. In such situations, each intermediate node routes the packets (e.g., data and control information) to the next node along the route, until the packets reach their final destination. For relaying packets to the next node, each node should maintain routing information collected through conversation with neighboring nodes. The routing information can also be periodically broadcast in the network to reflect the current network topology. Alternatively, to reduce the amount of information transmitted for maintaining accurate routing information, the network nodes may exchange routing information only when it is needed. In an approach known as Mesh Scalable Routing (MSR), described in U.S. Patent Application 20040143842 which is incorporated by reference herein in its entirety.
One access scheme for ad hoc networks is Time Division Multiple Access (TDMA), in which the transmission resource of a radio frequency is divided into time slots, and a unit may transmit in one or several time slots. This allows multiple user to share the same transmission medium (e.g. radio frequency) while using only part of its bandwidth. TDMA scheme is commonly used in digital cellular standards, satellite systems and local area networks. It is known that TDMA scheme works well for periodic and time sensitive traffic than Carrier Sense Multiple Access (CSMA). Most of the commonly used TDMA system works with centralized time slot allocation. For example, in cellular system, base station is central authority whereas in local area network, access point is the central node, which is responsible for allocation time slots for communication for all the attached nodes.
Centralized allocation of timeslots requires exchanging a large amount of network management information, which consumes valuable communication bandwidth. Centralized timeslot allocation techniques are typically applied in networks where the length of the communication path is relatively small (e.g., only one hop). Applying centralized timeslot allocation techniques in multi-hopping networks can be problematic because the of the significant amount of time required for propagating information from nodes at the periphery of the network to a central node, and for propagating information from the central node back to the nodes at the periphery of the network. Centralized timeslot allocation techniques are inefficient for reaching all network nodes due to mobility of nodes and the relatively long time needed for propagating the information to each node in the network. For this reason, in mobile multi-hopping networks, where the topology of nodes changes frequently, the utilization of centralized timeslot allocation techniques is prohibitive.
There can be multiple routes present between the nodes, but not all routes can support the quality of service (QoS) requirements of a particular data stream, this is especially true in systems employing TDMA Media Access Control (MAC) as routes may not even have sufficient slots to sustain the data stream. And hence there is a need to find out such a route and allocate appropriate time slots in a distributed fashion which can meet the QoS requirements of the data stream.
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